(1) Field of the Invention
This invention relates to an external skin care preparation, and more specifically to an external skin care preparation which can enhance the water-retaining ability of the horny layer and improve skin roughness.
(2) Description of the Related Art
The water content of the horny layer has already been known to be critical for imparting moisture to the skin to maintain the skin smoothness and softness. The retention of water is said to rely upon a water-soluble component contained in the horny layer, namely, a free amino acid, organic acid, urea or inorganic ions. These materials have been incorporated either singly or in combination in medical external skin care preparations or cosmetic preparations with a view toward improving or avoiding skin roughness.
Besides, many humectants having high affinity with water have also been developed and have been used for similar purposes.
However, these humectants remain on the skin surface when they are applied to the skin, so that they serve to supply water to horny layer. Moreover, their effects are temporary and they are not such that can improve the water-retaining ability of the horny layer and can also avoid or cure skin roughness substantially.